In the development of improved methodologies to meet the ever-increasing demands for the production of petroleum hydrocarbons, improved tubing systems have been developed for use at great drilling depths, in directionally drilled wells, and in ever increasing very corrosive high pressure and temperature operational environments. There are constant needs to meet such increasingly demanding reliability requirements under ever more stringent field conditions.
Two broadly different present categories of such improved systems are generally recognized, namely, those which, on the one hand, meet standards set by the American Petroleum Institute (API) and those which, on the other hand, meet specialized, usually more exacting standards, usually commercialized as “premium” products. The latter group is necessarily more costly, and seldom economically viable for general usage, so although the concepts presented here may find application in premium products, this invention is primarily directed to tubular goods that meet particularized API standards.
API standard products must meet known tolerances and design characteristics, so they are consequently interchangeable, less costly, and available in quantity. They are therefore preferred for use wherever field conditions permit. In order to gain the longest working life and best economic case, some API tubing and casing, when used in corrosive environments, are internally plastic coated (IPC) and others insert fiberglass liners (FGL). As technology has developed to extract oil from fields which are less accessible, more stressful conditions have had to be met and overcome, including operating at increasingly greater drilling depths and under even less favorable production conditions.
Different problems are presented by W/AG (water/alternating gas) systems for recovery of additional hydrocarbons by the injection of water and CO2 gas into fields in which production has dwindled to near nothing or which have otherwise ceased to produce. This has led to increasing adoption of the internally coated and fiberglass lined tubing systems, to provide tubing strings which not only can withstand high pressures and temperatures, but which can also resist corrosion and chemical attack. Placing such products in use, in turn, has revealed a number of other problems and weaknesses. For example, applying a protective coating adapted for its chemical resistance to attack often also led to threaded end area non-uniformities. Such coatings have to be applied by spraying, which more or less inevitably has tended to introduce disparities between coating thickness at the crest and root areas of the threads. Moreover, the stresses within a threaded joint vary with the local physical strength of segments of the joint, since the relatively thinner cross-sections of pin ends are likely to deflect more than the thicker opposing sections of the associated coupling sleeve during makeup and joint tightening. Minute but significant surface imperfections can then appear in the coatings and these imperfections can be attacked by pressurized corrosive gases. Moreover, continued or repeated makeup of a coupling may introduce hairline cracking which can affect not only the integrity of a coating or lining, but also the physical strength of a threaded joint. In consequence, even though the lined or coated tubing and coupling combinations are intended for repeated engagement and disengagement, these and other problems have militated against satisfactory performance under repeated use.
Workers in the art therefore have sought to introduce special techniques for improving sealing performance. Perhaps the most commonly used is a product called “Coupling Guard”™ a product of Tuboscope Inc. which is formulated of an epoxy, PTFE, and “Ryton”™, a liquid mix which is applied to an interior central length of the central region of a coupling and is subsequently thermally treated to accelerate solidification and curing. The liquid properties of the mix and the inherent shrinkage following the heating and curing process can introduce irregularities between the thickness of the thread crest coatings in comparison to the thickness at the thread roots. Consequently, there can be a proclivity toward thread damage under makeup conditions, and thread damage and deformation because of differentials in pin end radial compression. If stresses exceed the capability of a material beyond what it can resist, the deformation will introduce cracking of the plastic coating. Damage and loss of corrosion protection also occur from successive makeup and breakout of the connections.
Another connection for internally plastic coated pipe is sold by Hunting Energy Services, of Houston, Tex. as the “KC-MMS Connection”™ and uses an interior ring seal centrally set into an interior circumference of a coupling. The ring seal includes an index tongue on the coupling internal diameter and a matching outer groove on the outer surface of the seal. Tapered side wings on the ring engage the pin end faces inserted into the coupling. Central sealing requires both precision marking and subsequent makeup steps, often difficult to achieve under practical field circumstances. For example, the “KC-MMS Connection” must be aligned relative to “timing” or “makeup marks” on the connection, which alignment is time consuming and difficult to achieve in the field and if not performed properly can result in widely varying final makeup torque. Moreover, the “MMS” type of sealing connection can encounter problems during assembly, from hydraulic deformation and displacement of the thread lube as the pin is being driven into the coupling. Also, the thread lube can be forced into the space between the wing of the resilient seal and the coupling and impelled by hydraulic forces out of its groove.
These and other problems are exacerbated during production when high pressure injection tubing has to be withdrawn from the downhole installation and run back in, as for regular maintenance or replacement or repair. This is commonly known in the industry as “tripping the pipe”. It is preferred to be able to do this at least 8-10 times, although practical experience has shown that this is seldom feasible. This is true because such conditions as thread deformation, pin end compressive deformation and coupling bell-out exist and impede establishing the torque level in the connection that is needed for adequate strength.
Consequently, some existing very expensive premium internally plastic coated and fiberglass lined pipe connections have been designed to confront the problem of providing adequate pressure containment and corrosion resistance. However, economic and operative advantages can be realized if baseline, economical, API threaded and coupled connection products can be widely used under the previously stated more stringent conditions and still furnish all the operative reliability and repeatability that is required.